If you're using a Linux distro, chances are you're using LibreoOffice or at worst the latest release of Apache OpenOffice (which isn't technically dead, but on life support). If you use an Android smartphone, more than likely you're using WPS Office. If you're on Windows you probably clicked the "get MS Office" link that Microsoft pushes on all installs of Windows 10.
Pros and Cons:
For LibreOffice: really Free. Deals very well with both legacy and current file formats from any source. Interface is familiar, constantly improving and user-customizable. Same-day release on Windows, Linux and OS-X; Android still in the works, cloud version is still quite experimental. Cons: no VisualBasic support. Default interface still looks dated...